1. Field of the Invention
This invention pertains in general to use video compression technology to encode and decode information, and in particular, to provide an enhanced hybrid video coder using bitmap-mode coding.
2. Description of the Related Art
Video compression is useful for transmission of digital video over a variety of bandwidth-limited networks, or for storage constrained applications. For example, the broadcast transmission of digital video at 24-bit per pixel sampled at 720 by 480 spatial resolution and 30 frames per second (fps) temporal resolution would require a bit rate of above 248 Mbps! Taking another example of supporting web browser applications with rich media content in a client-server architecture within a wireless network, bandwidth limitations of the wireless network itself may comprise one of the major limiting factors in fully utilizing the client-server architecture. Client devices, such as mobile phones, may additionally be resource-constrained with respect to the device's capabilities, including processing power, memory and battery life limitations. Compounding this, web browser applications are continually embracing rich media content, such as digital video and audio, which in turn poses further challenges for a client-server architecture. For applications such as digital television broadcasting, satellite television, Internet video streaming, video conferencing and video security over a variety of networks, limited transmission bandwidth or storage capacity stresses the demand for higher video compression ratios.
To improve compression efficiency, currently available coding standards, such as MPEG-1, MPEG-2, MEPG4 and H.264/AVC etc., remove information redundancy spatially within a video frame and temporally between video frames. The goal of video compression systems is to achieve the best fidelity (or the lowest distortion D) given the capacity of a transmission channel, subject to the coding rate constraint R(D). However, this optimization task is complicated by the fact that various coding options show varying efficiency with different scene content and at different bit rates.
One limitation with conventional hybrid video coders such as a H.264 video coder is inefficiency at removing encoding noise especially around sharp edges. Such encoding noise, such as the mosquito artifacts, is easily noticeable to human eyes especially when browsing images that often contains text with a simple background, such as black text on a white background. For browsing images, the text embedded in the images needs to be encoded with high fidelity, but the simple background can afford more compression since not much data are contained in the background. To allow regions of an input picture to be represented without any loss of fidelity, H.264 video coding standard includes a “PCM” macroblock mode, in which the values of input pixels are sent directly from an encoder to a decoder without prediction, transformation or quantization. Additional motivation for this macroblock mode is to impose a minimum upper bound on the number of bits that can be used to represent a macroblock with sufficient accuracy. However, the PCM mode is not efficient to deal with encoding noise because an encoder can only choose to use PCM for high quality, at the expense of higher bit rate, or not use PCM for less high quality with a controlled bit rate for the encoder.
Hence, there is, inter alia, a lack of a system and method that provides an enhanced hybrid encoder within a video processing system.